A contactor of this character is the subject matter of my commonly owned prior U.S. Pat. No. 3,640,270. As disclosed in that prior patent, the contactor has a generally cup-shaped housing of nonmetallic material with a mouth bounded by a tissue-engaging rim; the housing contains an electrode which is recessed within the rim but accessible by way of its mouth so as to be able to make contact with the skin of a person or animal to be tested or treated. The mouth of the cup communicates with a low-pressure zone inside a conduit which is traversed by a flow of high-pressure gas, generally air, and is embedded in the elastomeric material of the housing. The low-pressure zone lies at the outlet of a Venturi nozzle accelerating the flow of gas which is discharged into the atmosphere at an open end of the conduit. The latter includes a metal tube which also forms part of a conductive connection between the external conduit, which may include a voltage source, and the electrode.
The electrode of the contactor described in that prior patent comprises a metallic plate carrying a sponge which is permeated by a liquid electrolyte and has an exposed skin-engaging surface. Another type of electrode suitable for such a device, described in commonly owned German Pat. No. 25 29 909, is a plate of coherent particles--sintered or simply pressed--of a mixture of silver and one or more silver salts such as silver chloride, silver bromide, silver iodide, silver rhodanide or silver cyanide. Such an electrode, which has the advantage of low contact resistance, must be protected from interaction with adjoining elements of different metallic materials which can give rise to detrimental local currents. It is for this reason that, as taught in the German patent referred to, a contact plate consisting of the aforedescribed compacted mixture of metallic silver and a silver salt is supported on a metallic body coated with silver at least in its area adjoining the plate. That German patent also shows a retaining screw which holds the contact plate onto the supporting body and consists at least on an outer surface of nonconductive material; a titanium screw, with an oxide layer on its surface, is particularly mentioned in this context. An electrode of this type, comprising a massive metallic supporting body made at least partly of silver, is relatively expensive.
Reference may also be made to another commonly assigned earlier U.S. patent of mine, No. 4,248,243, showing a contactor of the type here envisaged connected to a diagnostic apparatus such as an electrocardiograph.